JP2011220274A - Device for detection of failure in internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an failure detection device of an internal combustion engine that can detect a variation failure of an inter-cylinder air/fuel ratio irrespective of a state that the supply of fuel is cut and a state that the engine is under cylinder cut-off control.SOLUTION: A control device of the internal combustion engine can detect an air/fuel ratio of the exhaust gas of the engine by an air/fuel ratio sensor which is attached to an exhaust pipe assembly of a multi-cylinder engine, and detects the air/fuel ratio. The control device includes a multi-cylinder air/fuel ratio calculator which partially operates average air/fuel ratios of amounts of the plurality of cylinders which are continued during normal operation by combining all the cylinders, compares the average air/fuel ratios of injection amounts of the plurality of cylinders which are obtained by the multi-cylinder air/fuel ratio calculator, determines the variation failure of the inter-cylinder air/fuel ratio, and also performs correction.

Description

  In the present invention, an air-fuel ratio sensor is installed in an exhaust gas merging portion (hereinafter referred to as an “exhaust merging portion”) of an internal combustion engine (engine) having a plurality of cylinders, and the air-fuel ratio of the plurality of cylinders is determined based on the air-fuel ratio sensor output. More specifically, the present invention relates to an abnormality diagnosis technique for an inter-cylinder air-fuel ratio control system.

  In recent years, in an engine for a vehicle, a single air-fuel ratio installed in an exhaust gas merging section of a plurality of cylinders in order to accurately detect an abnormal variation in the air-fuel ratio between cylinders of an internal combustion engine, which causes deterioration in emissions and fuel consumption. An inter-cylinder air-fuel ratio control technique has been proposed in which the air-fuel ratio of a plurality of cylinders is estimated for each cylinder based on the output of a sensor and the air-fuel ratio (fuel injection amount) of the plurality of cylinders is controlled for each cylinder (for example, a patent Reference 1).

  In the above-mentioned patent document 1, some cylinders among a plurality of cylinders are deactivated (hereinafter referred to as “cylinder reduction control”), and the operation other than the deactivated cylinder is performed with the intake port and / or the exhaust port of the deactivated cylinder closed. A technique for detecting an abnormal variation in the air-fuel ratio between cylinders based on the output of the air-fuel ratio sensor in the middle cylinder is shown.

  However, in order to detect an abnormal variation in the air-fuel ratio between cylinders, it is necessary to install a special mechanism for stopping the injection for each cylinder, and avoiding torque shock and dribbling deterioration caused by stopping the injection for each cylinder. In order to do this, it is necessary to limit the operating state in which the abnormality diagnosis is executed.

JP 2009-24531 A

  The conventional abnormality detection device for an internal combustion engine is based on the technology described in Patent Document 1 only for some vehicles equipped with a valve device that can stop the opening / closing operation of an intake port and / or an exhaust port independently for each cylinder. Therefore, there is a problem that it cannot be applied to an internal combustion engine of many vehicles not equipped with such a valve device.

  In addition, because some cylinders are deactivated at the time of abnormality diagnosis, in order to avoid torque shock and deterioration of drivability when the engine is deactivated at normal times, the abnormality diagnosis is executed under conditions such as fuel cut or reduced cylinder control. Since the conditions are required, there is a problem that execution conditions for abnormality diagnosis are limited.

  The present invention has been made to solve the above-described problems, and can be applied to a vehicle that is not equipped with a valve device that can be stopped independently for each cylinder. An object of the present invention is to obtain an abnormality detection device for an internal combustion engine that is capable of detecting an abnormality in the variation in the air-fuel ratio between cylinders, not only during fuel cut or during cylinder reduction control.

  An abnormality detection apparatus for an internal combustion engine according to the present invention includes a linear air-fuel ratio sensor that is attached to an exhaust pipe assembly of an engine having a plurality of cylinders and detects an air-fuel ratio of exhaust gas from the engine, and a detection value of the linear air-fuel ratio sensor. Based on this, the variation in the air-fuel ratio between cylinders is detected by comparing the average air-fuel ratio with the multiple-cylinder air-fuel ratio calculating means for calculating the average air-fuel ratio for consecutive multiple cylinder injections for all cylinder combinations. And an inter-cylinder air-fuel ratio abnormality detecting means, and an inter-cylinder air-fuel ratio abnormality detecting means for correcting an inter-cylinder air-fuel ratio abnormality abnormality when the inter-cylinder air-fuel ratio abnormality detecting means detects abnormality in the inter-cylinder air-fuel ratio. It is provided.

  According to the present invention, the intake port and / or the exhaust port for each cylinder can be applied to a vehicle that is not equipped with a valve device that can stop the opening / closing operation independently for each cylinder. It is possible to detect an abnormality in the variation of the air-fuel ratio between cylinders, not only during the time or during the cylinder reduction control.

1 is a configuration diagram schematically showing an internal combustion engine system to which an abnormality detection device for an internal combustion engine according to Embodiment 1 of the present invention is applied. FIG. It is a block diagram which shows specifically the engine in FIG. 1 is a block diagram specifically showing an ECU according to Embodiment 1 of the present invention. FIG. 3 is a flowchart showing an abnormality detection operation for an air-fuel ratio between cylinders according to Embodiment 1 of the present invention. FIG. 4 is an explanatory diagram schematically showing the operation of the multiple cylinder air-fuel ratio calculating means in FIG. 3. 4 is a flowchart showing specific operations of a plurality of cylinder air-fuel ratio calculating means, an inter-cylinder air-fuel ratio abnormality detecting means, and an inter-cylinder air-fuel ratio correcting means in FIG. 7 is a flowchart showing specific operations of a multi-cylinder air-fuel ratio calculating means, an inter-cylinder air-fuel ratio abnormality detecting means, and an inter-cylinder air-fuel ratio correcting means according to Embodiment 2 of the present invention.

Embodiment 1 FIG.
Embodiment 1 of the present invention will be described below with reference to the drawings.
1 is a block diagram schematically showing an internal combustion engine system to which an abnormality detection apparatus for an internal combustion engine according to Embodiment 1 of the present invention is applied.
In FIG. 1, an engine 1 detects a crank angle sensor 2 for detecting a crank angle, a cam angle sensor 3 for detecting a cam angle, and an engine cooling water temperature as various sensors for detecting an engine load and an engine state. A water temperature sensor 4 is installed.

  Further, on the intake side of the engine 1, as various other sensors, an airflow sensor 7 for detecting the intake amount of the intake air A, a throttle sensor 9 for detecting the opening degree of the throttle 8, and downstream of the throttle 8. A pressure sensor 11 for detecting the pressure in the suction passage 10 on the side and an intake air temperature sensor 12 for detecting the temperature of the intake air A are provided.

  Further, in the exhaust passage 15 of the engine 1, as various other sensors, a linear air-fuel ratio sensor (hereinafter also referred to as “LAFS”) 16 that detects the air-fuel ratio of the exhaust gas B and a three-way catalyst 17 after passing through A rear O2 sensor 18 for detecting the oxygen concentration in the exhaust gas C is installed.

  On the other hand, the engine 1 is provided with an ignition coil 5 that generates a high voltage and an ignition plug 6 that generates a spark in a cylinder of the engine 1 as various actuators that are driven and controlled by an ECU (electronic control unit) 19. ing.

Further, on the intake side of the engine 1, as various other actuators, a throttle 8 for adjusting the intake amount, an injector 13 for injecting fuel into the intake air A sucked into the cylinder, and fuel to the injector 13 A fuel pump 14 to be supplied is installed.
Further, a three-way catalyst 17 for purifying the exhaust gas C is installed in the exhaust passage 15 of the engine 1.

  The ECU 19 is supplied with power from an in-vehicle battery 20, and calculates various control amounts using the crank signal from the crank angle sensor 2, the cam signal from the cam angle sensor 3, and other various sensor signals as input information. The engine 1 (internal combustion engine) is controlled by driving various actuators such as the ignition coil 5, the throttle 8 and the injector 13.

FIG. 2 is a configuration diagram specifically showing the engine 1 in FIG. 1, and schematically shows the attachment position of the LAFS 16 taking the case of an in-line four-cylinder engine as an example.
In FIG. 2, individual injectors 13 are installed on the intake side of the cylinders # 1 to # 4.

A single LAFS 16 for detecting the air-fuel ratio of the exhaust gas B is attached to the exhaust merging portion of each exhaust passage 15 of the cylinders # 1 to # 4.
The ECU 19 calculates the fuel injection amount for each cylinder based on the air-fuel ratio information from the LAFS 16 and various sensor information, and drives and controls the injector 13 for each cylinder.

FIG. 3 is a block diagram specifically showing the ECU 19 in FIG. 1, and shows a functional configuration of a main part of the abnormality detection device for an internal combustion engine according to Embodiment 1 of the present invention.
In FIG. 3, the ECU 19 includes, as main functions of the abnormality detection device for the internal combustion engine, a diagnosis execution condition determination unit 301, a multi-cylinder air-fuel ratio calculation unit 302, an inter-cylinder air-fuel ratio abnormality detection unit 303, and an inter-cylinder air-fuel ratio correction. Means 304.

Further, the ECU 19 includes a target air-fuel ratio calculation unit 306 and an air-fuel ratio correction amount calculation unit 307 as functions of a normal air-fuel ratio feedback control device.
The target air-fuel ratio calculating means 306 calculates a target air-fuel ratio based on detection information (operation state of the engine 1) of various sensors 300.

  The air-fuel ratio correction amount calculation means 307 calculates the air-fuel ratio correction amount based on the deviation between the air-fuel ratio detected by the LAFS 16 and the target air-fuel ratio, and contributes to the feedback control of the injector 13. The air-fuel ratio correction amount is also input to the inter-cylinder air-fuel ratio abnormality detecting means 303 as necessary.

The diagnosis execution condition determination unit 301 determines whether or not the operation state of the engine 1 satisfies a condition capable of executing the abnormality detection process based on the detection information of the various sensors 300. The calculation means 302 and the inter-cylinder air-fuel ratio abnormality detection means 303 are validated.
To do.

The multi-cylinder air-fuel ratio calculating means 302 calculates the average value (average air-fuel ratio) of the air-fuel ratios for the three cylinders based on the detection information of the crank angle sensor 2, the cam angle sensor 3, and the LAFS 16.
The cylinder-to-cylinder air / fuel ratio abnormality detecting unit 303 detects an abnormality in the variation of the cylinder / cylinder air / fuel ratio using the average air / fuel ratio of the three cylinders obtained by the multi-cylinder air / fuel ratio calculating unit 302.
It has.

  The inter-cylinder air-fuel ratio correcting means 304 corrects the fuel injection amount and eliminates the air-fuel ratio fluctuations for the cylinders in which the inter-cylinder air-fuel ratio abnormality detecting means 303 detects the abnormal abnormality in the inter-cylinder air-fuel ratio. The drive control amount of the injector 13 for each cylinder is optimally corrected.

Next, the abnormality detection operation of the air-fuel ratio between cylinders according to the first embodiment of the present invention shown in FIGS. 1 to 3 will be described with reference to the flowchart of FIG. 4 and the explanatory diagram of FIG.
In FIG. 3, first, the diagnosis execution condition determination unit 301 determines whether or not the operating state of the engine 1 is in a state where abnormality in variation in the air-fuel ratio between cylinders can be detected (diagnosis execution condition is established) (step 401).

Specifically, for example, with respect to operation information such as intake air intake amount, engine speed, throttle opening, etc., each deviation amount during a predetermined period is monitored, and each deviation amount is small (indicating a steady operation state). In addition, it can be determined that the diagnosis execution condition is satisfied.
Note that it is necessary to perform monitoring under the same conditions during the period from when the diagnosis execution condition is satisfied to when the diagnosis execution is completed, so it is desirable to stop the normal fuel feedback control based on the LAFS 16.

If it is determined in step 401 that the diagnosis execution condition is not satisfied (that is, NO), the processing routine of FIG. 4 is terminated.
On the other hand, if it is determined in step 401 that the diagnosis execution condition is satisfied (that is, YES), the multi-cylinder air-fuel ratio calculating means 302 excludes one of the four cylinders # 1 to # 4 during normal operation. The average air-fuel ratio for the three cylinders is calculated for the combination of all the cylinders (step 402).

FIG. 5 is an explanatory diagram schematically showing the operation of the multi-cylinder air-fuel ratio calculating means 302. The patterns (1) to (4) of the calculation target cylinders (three cylinders) among the in-line four cylinders # 1 to # 4 are shown. Show.
In FIG. 5, white circles and black circles arranged corresponding to # 1, # 3, # 4, and # 2 in order from the left mean the normal injection order, and the average empty for the cylinders corresponding to the black circles. It means that the fuel ratio is calculated.

In each of the patterns (1) to (4), the calculation target of the average air-fuel ratio is 3 cylinders each.
That is, in pattern (1), the average air-fuel ratio of the three cylinders # 3, # 4, and # 2 is calculated, and in pattern (2), the average air-fuel ratio of the three cylinders # 4, # 2, and # 1 is calculated. In pattern (3), the average air-fuel ratio of the three cylinders # 2, # 1, and # 3 is calculated. In pattern (4), the average air-fuel ratio of the three cylinders # 1, # 3, and # 4 is calculated. To do.

In step 402, the multi-cylinder air-fuel ratio calculating means 302 calculates the average air-fuel ratio for each of the three cylinders using a total of four patterns shown in FIG.
In order to further improve the accuracy, the respective calculations of the patterns (1) to (4) may be integrated a predetermined number of times, and an average value of the integrated values may be obtained and used in the subsequent calculations.

Subsequently, the inter-cylinder air / fuel ratio abnormality detecting means 303 determines the presence / absence of an abnormal variation in the inter-cylinder air / fuel ratio from the average air / fuel ratio of the three cylinders calculated in step 402 (step 403).
If it is determined in step 403 that there is no abnormality in variation in the air-fuel ratio between cylinders (that is, NO), the processing routine of FIG. 4 is terminated.

  On the other hand, if it is determined in step 403 that there is an abnormal variation in the air-fuel ratio between cylinders (that is, YES), the air-fuel ratio correcting means 304 between cylinders corrects the fuel injection amount to the cylinder determined to be abnormal, The fuel injection amount reflecting the correction amount is calculated (step 404), and the processing routine of FIG. 4 is terminated.

Hereinafter, the injector 13 supplies a fuel injection amount reflecting the correction amount to the target cylinder.
On the other hand, if the diagnosis execution condition is not satisfied in step 401 (NO), or if the variation in the air-fuel ratio between cylinders is determined to be normal (NO) in step 403, the fuel injection amount is not executed without executing the correction calculation in step 404. Is calculated, and the injector 13 supplies a fuel injection amount that is not corrected to the target cylinder.

Next, specific processing in steps 402 to 404 in FIG. 4 will be described with reference to FIG. 6 together with FIG.
FIG. 6 is a flowchart showing specific operations of the multi-cylinder air-fuel ratio calculating means 302, the inter-cylinder air-fuel ratio abnormality detecting means 303, and the inter-cylinder air-fuel ratio correcting means 304.

In FIG. 6, first, the multi-cylinder air-fuel ratio calculating means 302 calculates an average air-fuel ratio for three cylinders of the patterns (1) to (4) shown in FIG. Input to means 303.
Subsequently, in the inter-cylinder air / fuel ratio abnormality detecting means 303, first, the average air / fuel ratios of the patterns (1) to (4) satisfy the relationship “(3) = (4) = (2) ≠ (1)”. Whether or not (step 602).

Here, the equal sign “=” means that the difference in average air-fuel ratio for the three cylinders is within a predetermined range, and the inequality sign “≠” means that the difference in average air-fuel ratio is outside the predetermined range. Means.
Therefore, in step 602, whether the average air-fuel ratio of each pattern (3), (4), (2) shows a substantially equivalent value and only the average air-fuel ratio of pattern (1) shows a different value (abnormal)? Determine whether or not.

If it is determined in step 602 that the relationship of “(3) = (4) = (2) ≠ (1)” is satisfied (that is, YES), the pattern (3) including the # 1 cylinder, ( 4) Since there is a difference between (2) and the pattern (1) not including the # 1 cylinder, it is determined that the # 1 cylinder is abnormal (step 603).
Thereafter, the inter-cylinder air-fuel ratio correcting unit 304 corrects the # 1 cylinder to be lean or rich (step 611), and ends the processing routine of FIG.

On the other hand, if it is determined in step 602 that the relationship of “(3) = (4) = (2) ≠ (1)” is not satisfied (that is, NO), then the inter-cylinder air / fuel ratio abnormality detecting means 303 is continued. Determines whether the average air-fuel ratio satisfies the relationship of “(1) = (4) = (2) ≠ (3)” (step 604).
In step 604, it is determined whether or not the average air-fuel ratios of patterns (1), (4), and (2) show substantially the same value, and only the average air-fuel ratio of pattern (3) shows a different value.

If it is determined in step 604 that the relationship of “(3) = (4) = (2) ≠ (3)” is satisfied (that is, YES), the pattern (1) including the # 3 cylinder, ( 4) Since there is a difference between (2) and the pattern (3) not including the # 3 cylinder, the # 3 cylinder is determined to be abnormal (step 605).
Thereafter, the inter-cylinder air-fuel ratio correcting means 304 corrects the # 3 cylinder to be lean or rich (step 611), and ends the processing routine of FIG.

On the other hand, if it is determined in step 604 that the relationship of “(1) = (4) = (2) ≠ (3)” is not satisfied (that is, NO), then the inter-cylinder air / fuel ratio abnormality detecting means 303 is continued. Determines whether the average air-fuel ratio satisfies the relationship of “(1) = (3) = (2) ≠ (4)” (step 606).
In step 606, it is determined whether or not the average air-fuel ratios of the patterns (1), (3), and (2) show substantially the same value, and only the average air-fuel ratio of the pattern (4) shows a different value.

If it is determined in step 606 that the relationship of “(1) = (3) = (2) ≠ (4)” is satisfied (that is, YES), the pattern (1) including the # 4 cylinder, ( 3) Since there is a difference between (2) and the pattern (4) not including the # 4 cylinder, the # 4 cylinder is determined to be abnormal (step 607).
Thereafter, the inter-cylinder air-fuel ratio correcting means 304 corrects the # 4 cylinder to be lean or rich (step 611), and ends the processing routine of FIG.

On the other hand, if it is determined in step 606 that the relationship of “(1) = (3) = (2) ≠ (4)” is not satisfied (that is, NO), then the inter-cylinder air / fuel ratio abnormality detecting means 303 is continued. Determines whether the average air-fuel ratio satisfies the relationship of “(1) = (3) = (4) ≠ (2)” (step 608).
In step 608, it is determined whether or not the average air-fuel ratios of patterns (1), (3), and (4) show substantially the same value, and only the average air-fuel ratio of pattern (2) shows a different value.

If it is determined in step 608 that the relationship of “(1) = (3) = (4) ≠ (2)” is satisfied (that is, YES), the pattern (1) including the # 2 cylinder, ( 3) Since there is a difference between (4) and the pattern (2) not including the # 2 cylinder, it is determined that the # 2 cylinder is abnormal (step 607).
Thereafter, the inter-cylinder air-fuel ratio correcting unit 304 corrects the # 2 cylinder to be lean or rich (step 611), and ends the processing routine of FIG.

  On the other hand, if it is determined in step 608 that the relationship of “(1) = (3) = (4) ≠ (2)” is not satisfied (that is, NO), it does not apply to any abnormal pattern. The inter-cylinder air / fuel ratio abnormality detecting means 303 determines that the variation in the inter-cylinder air / fuel ratio is normal (step 610), and ends the processing routine of FIG.

In step 611, the inter-cylinder air-fuel ratio correcting unit 304 corrects the variation in the inter-cylinder air-fuel ratio from the calculation results of the multi-cylinder air-fuel ratio calculating unit 302 and the inter-cylinder air-fuel ratio abnormality detecting unit 303.
That is, when the # 1 cylinder is abnormal, the rich / lean relationship between the patterns (3), (4), (2) including the # 1 cylinder and the pattern (1) not including the # 1 cylinder is determined, When the pattern including # 1 cylinder is richer, the cylinder # 1 is corrected to the lean side, and when the pattern including # 1 cylinder is leaner, the cylinder # 1 is corrected to the rich side. Correct the variation in the air-fuel ratio.

Note that the inter-cylinder air / fuel ratio abnormality detecting means 303 compares the patterns (3), (4), (2) including the # 1 cylinder with the pattern (1) not including the # 1 cylinder in step 602, for example. However, the pattern including the # 1 cylinder may be compared with the target air-fuel ratio.
In this case, the inter-cylinder air / fuel ratio correcting means 304 compares the pattern including the # 1 cylinder with the target air / fuel ratio, and corrects the # 1 cylinder to the lean side when the pattern including the # 1 cylinder is richer. When the pattern including the # 1 cylinder is leaner, the variation in the air-fuel ratio between the cylinders is corrected by correcting the # 1 cylinder to the rich side.

  As described above, the abnormality detection apparatus for an internal combustion engine according to Embodiment 1 (FIGS. 1 to 6) of the present invention is attached to an exhaust pipe assembly portion of an engine 1 having a plurality of cylinders # 1 to # 4. Based on the linear air-fuel ratio sensor 16 that detects the air-fuel ratio of one exhaust gas B, and the detected value of the linear air-fuel ratio sensor 16, the average air-fuel ratio for consecutive multiple cylinder injections is calculated for the combination of all cylinders. The multi-cylinder air-fuel ratio calculating unit 302 compares the average air-fuel ratio with each other to detect a variation in the inter-cylinder air-fuel ratio, and the inter-cylinder air-fuel ratio abnormality detecting unit 303 detects the variation between the cylinders. Inter-cylinder air-fuel ratio correcting means 304 is provided for correcting the variation in the air-fuel ratio between cylinders when an abnormality in the air-fuel ratio variation is detected.

  In this way, the cylinder in which the variation in the air-fuel ratio between the cylinders is abnormal is determined, and the cylinder in which the abnormality is detected is determined based on the comparison result of the average air-fuel ratios calculated by the multiple-cylinder air-fuel ratio calculation means 302. By correcting the variation in the air-fuel ratio, the intake port and / or exhaust port for each cylinder can be applied to a vehicle that is not equipped with a valve device that can stop the opening / closing operation independently for each cylinder. Thus, it is possible to obtain an abnormality detection device for an internal combustion engine that can detect an abnormality in the variation of the air-fuel ratio between cylinders and correct it during normal operation, not only during fuel cut or during cylinder reduction control.

  Further, as shown in FIG. 3, various sensors for detecting the operating state of the engine 1, target air-fuel ratio calculating means 306 for calculating a target air-fuel ratio based on detection information of the various sensors, and detection values of the linear air-fuel ratio sensor 16 Air-fuel ratio correction amount calculating means 307 for calculating the air-fuel ratio correction amount based on the deviation from the target air-fuel ratio, and the inter-cylinder air-fuel ratio abnormality detecting means 303 is an air-fuel ratio correction amount or a learned value of the air-fuel ratio correction amount. From this, the average air-fuel ratio can be calculated to detect variations in the air-fuel ratio between cylinders.

Embodiment 2. FIG.
In the first embodiment (FIG. 6), the abnormality is determined based on the comparison of the average air-fuel ratios. However, as shown in FIG. 7, the variation abnormality is considered in consideration of the maximum value and the minimum value in each average air-fuel ratio. May be determined.

FIG. 7 is a flowchart showing a variation abnormality detection operation according to the second embodiment of the present invention. Similar to the above (FIG. 6), the multi-cylinder air-fuel ratio calculation means 302 and the inter-cylinder air-fuel ratio abnormality detection means 303 in FIG. The processing operation of the inter-cylinder air-fuel ratio correcting means 304 is shown.
The basic configuration and operation of the second embodiment of the present invention are as shown in FIGS.

In FIG. 7, steps 701 and 703 are the same processing as steps 601 and 610 described above (FIG. 6).
First, the multi-cylinder air-fuel ratio calculating means 302 calculates the average air-fuel ratio of each of the patterns (1) to (4) as described above (step 701).

Subsequently, the inter-cylinder air-fuel ratio abnormality detecting means 303 uses the average air-fuel ratio for the three cylinders of each pattern (1) to (4) as input information, and the average air-fuel ratio for the three cylinders of (1) to (4). The maximum value and the minimum value are calculated, and it is determined whether or not the deviation ΔAF between the maximum air-fuel ratio and the minimum air-fuel ratio is equal to or greater than a predetermined value (allowable range) (step 702).
If it is determined in step 702 that the deviation ΔAF is less than the predetermined value (that is, NO), it is determined that the deviation is normal (step 703), and the processing routine of FIG.

On the other hand, if it is determined in step 702 that the deviation ΔAF is greater than or equal to a predetermined value (that is, YES), the magnitude relationship of the air-fuel ratio of each cylinder is estimated from the average air-fuel ratio for the three cylinders (step 704).
For example, if the average air-fuel ratio for the three cylinders of patterns (1) to (4) in FIG. 5 is (1) → (3) → (4) → (2) in descending order, three cylinders From the magnitude relation of the average air-fuel ratio pattern of the minute, the magnitude relation of the air-fuel ratio of each cylinder can be estimated as follows.

  Considering the patterns (1) and (3), the # 4 cylinder and the # 2 cylinder are common and (1)> (3). Therefore, the magnitude relationship of the air-fuel ratio is # 3> # It turns out that it is 1.

  Similarly, considering the patterns (3) and (4), the # 2 cylinder and the # 1 cylinder are common, and (3)> (4). It can be seen that 4> # 3.

Further, considering the patterns (4) and (2), since the # 1 cylinder and the # 3 cylinder are common and (4)> (2), the magnitude relationship of the air-fuel ratio is # 2. It can be seen that># 4.
As a result, in step 704, it is estimated that the magnitude relationship between the air-fuel ratios of the cylinders is # 2>#4>#3># 1.

Next, the inter-cylinder air-fuel ratio abnormality detecting means 303 determines the deviation between the maximum value and the minimum value among the average air-fuel ratios of the three cylinders of the patterns (1) to (4) with respect to the target air-fuel ratio. It is determined whether the absolute value is large (step 705).
That is, in step 705, the absolute value of the deviation ΔAFmax between the maximum air-fuel ratio in the patterns (1) to (4) and the target air-fuel ratio becomes the minimum air-fuel ratio in the patterns (1) to (4) and the target. It is determined whether or not the deviation ΔAFmin from the air-fuel ratio is larger than the absolute value.

If it is determined in step 705 that | ΔAFmax |> | ΔAFmin | (that is, YES), the cylinder with the maximum air-fuel ratio estimated in step 704 is determined as a variation abnormal cylinder (step 706).
Thereafter, the inter-cylinder air-fuel ratio correcting unit 304 corrects the variation abnormality cylinder to the rich side (step 707) and ends the processing routine of FIG.

On the other hand, if it is determined in step 705 that | ΔAFmax | ≦ | ΔAFmin | (that is, NO), the cylinder having the minimum air-fuel ratio estimated in step 704 is determined as a variation abnormality cylinder (step 708).
Thereafter, the inter-cylinder air-fuel ratio correcting unit 304 corrects the variation abnormal cylinder to the lean side (step 709), and ends the processing routine of FIG.

The above processing (steps 701 to 709) is repeatedly executed until normality determination (step 703) is established.
Thereby, the dispersion | variation in the air-fuel ratio between cylinders can be made very small.

  As described above, according to the second embodiment (FIG. 7) of the present invention, the inter-cylinder air-fuel ratio abnormality detecting means 303 estimates the magnitude relation of the air-fuel ratio for each cylinder based on each average air-fuel ratio, and the air-fuel ratio. Since the variation in the air-fuel ratio between the cylinders can be detected from the correlation between the magnitude relationship between the average air-fuel ratio and the average air-fuel ratio, in addition to the effects similar to those of the first embodiment, Further suppression can be achieved.

  Similarly to the above, the inter-cylinder air-fuel ratio abnormality detecting means 303 can also calculate an average value for the injection of a plurality of cylinders from the air-fuel ratio correction amount or the learned value thereof, and detect an abnormal variation in the inter-cylinder air-fuel ratio. .

  In the first and second embodiments, the average air-fuel ratio for three cylinders is calculated by the multi-cylinder air-fuel ratio calculating means 302. However, the present invention is not limited to this, and the air-fuel ratio correction amount for three cylinders is calculated. An average value or an average value of learning values for three cylinders may be calculated. Also in this case, the inter-cylinder air-fuel ratio abnormality detecting means 303 and the inter-cylinder air-fuel ratio correcting means 304 can detect and correct the variation abnormality of the inter-cylinder air-fuel ratio.

  The present invention is not limited to the first and second embodiments, and can be applied to, for example, an internal combustion engine having four or more cylinders, and various modifications can be made without departing from the scope of the invention. .

  1 engine, 2 crank angle sensor, 3 cam angle sensor, 4 water temperature sensor, 5 ignition coil, 6 spark plug, 7 air flow sensor, 8 throttle, 9 throttle sensor, 10 intake passage, 11 pressure sensor, 12 intake air temperature sensor, 13 Injector, 14 Fuel pump, 15 Exhaust passage, 15 Exhaust passage, 16 Linear air-fuel ratio sensor, 17 Three-way catalyst, 18 Rear O2 sensor, 20 Battery, 300 Various sensors, 301 Diagnosis execution condition determination means, 302 Multi-cylinder air-fuel ratio Arithmetic means, 303 inter-cylinder air-fuel ratio abnormality detecting means, 304 inter-cylinder air-fuel ratio correcting means, 306 target air-fuel ratio calculating means, 307 air-fuel ratio correction amount calculating means, A intake air, B exhaust gas.

Claims (3)

A linear air-fuel ratio sensor that is attached to an exhaust pipe assembly of an engine having a plurality of cylinders and detects an air-fuel ratio of the exhaust gas of the engine;
Multi-cylinder air-fuel ratio calculating means for calculating an average air-fuel ratio for continuous multiple-cylinder injection based on a detection value of the linear air-fuel ratio sensor by a combination of all cylinders;
An inter-cylinder air-fuel ratio abnormality detecting means for detecting a variation in the inter-cylinder air-fuel ratio by comparing each of the average air-fuel ratios;
Abnormality detection of an internal combustion engine comprising: apparatus.   The inter-cylinder air-fuel ratio abnormality detecting means estimates the air-fuel ratio magnitude relationship for each cylinder based on the average air-fuel ratio, and from the correlation between the air-fuel ratio magnitude relationship and the average air-fuel ratio magnitude, The abnormality detection device for an internal combustion engine according to claim 1, wherein a variation in the air-fuel ratio is detected. Various sensors for detecting the operating state of the engine;
Target air-fuel ratio calculating means for calculating a target air-fuel ratio based on detection information of the various sensors;
Air-fuel ratio correction amount calculating means for calculating an air-fuel ratio correction amount based on a deviation between the detected value of the linear air-fuel ratio sensor and the target air-fuel ratio;
The inter-cylinder air-fuel ratio abnormality detecting means calculates the average air-fuel ratio from the air-fuel ratio correction amount or a learned value of the air-fuel ratio correction amount, and detects variations in the inter-cylinder air-fuel ratio. The abnormality detection device for an internal combustion engine according to claim 1 or 2.

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